Early reference to the idea of using a weightless environment for medical purposes.

"Now, Anti, don't be cynical. Doctors have an economic sense as well as the next person," said Docchi gravely. He turned to Cameron. "You see, after Anti grew too massive for her skeletal structure, doctors reasoned she'd be most comfortable in the absence of gravity. That was in the early days, before successful ship gravital units were developed. They put her on an interplanetary ship and kept transferring her before each landing.